Up until July, 1934, the job of policing the films out of Hollywood was mostly left up to Hollywood. There was no rating system and practically anything might appear in movies. While not extremely common, nudity, adultery, abortion, homosexuality and promiscuity were featured in quite a few pictures...including in Biblical epics such as "Ben Hur" (1925) and "The Sign of the Cross". Often, when folks use the term 'pre-code' they are usually referring to the more extreme films of this era...and "Laughter" clearly is a pre-code plot, as its main theme is adultery.
When the film begins, you learn that Peggy (Nancy Carroll) has married a rich guy (Frank Morgan). But she also has had some admirers--including a suicidal artist and one lover (Frederic March) who stops by for a visit! Now Peggy must decide whether she wants to stay married to the rich man or run off with fun-loving Paul.
Post 1934, such plots clearly would NOT have been allowed until, perhaps, the 1960s. The notion of an old boyfriend showing up and the young wife going off with him to spend a day with him was just too broadminded for the post-code days...and hard to believe that the husband would just sit back and allow this outing to take place. It is, however, reasonably interesting to watch though not the comedy I expected (IMDB called it a comedy romance...but there were very few laughs). Worth your time...especially if you are a pre-code fan but not a fan I'd rush to see either.